1. Field of the Invention
This invention relates to a process for producing a lactam copolymer having excellent impact strength by copolymerizing omega-lactam and a diene polymer in accordance with the technique of alkali polymerization of omega-lactam.
This invention also relates to a novel lactam copolymer having excellent impact strength produced by copolymerizing omega-lactam and a diene polymer in accordance with the technique of alkali polymerization omega-lactam.
This invention further relates to an article, particularly an automobile part, composed of the aforesaid copolymer.
2. Description of the Prior Art
The technique of polymerizing omega-lactam by the action of an aklaline catalyst and a co-catalyst, i.e. the so-called alkali polymerization method, is known. A polyamide obtained by this method has excellent mechanical strengths such as tensile strength, flexural strength and initial modulus, and is used as machine parts and industrial materials. However, it cannot be used in applications requiring flexibility since it has low elongation and impact strength and is hard and brittle.
Some methods have previously been proposed for the production of a polyamide/diene-type polymer copolymer in an attempt to improve the impact strength of the polyamide obtained by the alkali polymerization of omega-lactam.
For example, Japanese Patent Publication No. 15319/1977 discloses a process for producing a polyamide/polybutadiene copolymer having impact strength which comprises copolymerizing omega-lactam with a butadiene homopolymer or a copolymer of butadiene and a vinyl compound each having hydroxyl groups at both molecular ends by the action of an alkaline catalyst and a polyisocyanate. The copolymer obtained by this process, however, has inferior heat resistance since it contains a urethane linkage resulting from the reaction of the polyisocyanate and polybutadiene in the molecular chains. Another defect is that because the urethane linkage is readily hydrolyzed by the action of the alkaline catalyst, an increase in the amount of the polybutadiene in the polymer does not lead to a significant increase in the impact strength of the resulting copolymer.
Japanese Patent Publication No. 43756/1977 discloses a process for producing a polyamide/polybutadiene copolymer having impact strength which comprises polymerizing omega-lactam by the action of an alkaline catalyst and a polymerization activator obtained by the reaction of a butadiene homopolymer or butadiene/acrylonitrile copolymer having carboxyl groups at molecular ends with a diisocyanate. This process, however, requires an extra step of producing the polymerization activator from a carboxyl-containing butadiene polymer and a diisocyanate prior to the alkali polymerization of omega-lactam. The resulting polymerization activator has a very high viscosity and lends itself to difficult handling so that, for example, a long period of time is required in dissolving it in omega-lactam. This is industrially disadvantageous. Moreover, the impact strength of the resulting copolymer is not as high as is satisfactory.
U.S. Pat. No. 4,031,164 discloses a process for producing a lactam/polyol/polyacyl lactam terpolymer having excellent impact strength by utilizing the method of alkali polymerization of omega-lactam.
U.S. Pat. No. 4,490,520 discloses a process for producing a polyamide having improved impact strength, which comprises polymerizing lactam in the presence of an alkaline catalyst and the reaction product of a polyfunctional co-catalyst and a polyoxyalkyleneamine.
Molded articles prepared from the polyamides produced by these processes have the defect of being limited in uses because they have a high rate of water absorption and change greatly in size within short periods of time owing to water absorption.